Groove-Less Piston and Tapered Press Fit Hydraulic Lash Adjuster

ABSTRACT

A pushrod assembly for an engine is disclosed. The pushrod assembly may include a first piece configured to house a hydraulic lash adjuster and a second piece coupled to the first piece. The first piece may include a mating portion with a tapered end section. The second piece may include a first bore adapted to receive the mating portion of the first piece.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to internal combustion engines and, more particularly, to valve train components for an internal combustion engine.

BACKGROUND OF THE DISCLOSURE

Internal combustion engines, such as diesel or gasoline engines, generally include a valve train. The valve train regulates the motion of engine valves, which are used to control the flow of combustion and exhaust gases into and out of each engine cylinder. Among the numerous components of valve trains, a pushrod may be used to convert rotating motion of the camshaft into linear motion of the individual valves on each engine cylinder.

During engine operation, the increase in temperature may cause thermal expansion, elongating valve train components, such as pushrods. Thermal expansion and wear of the valve train components may result in unintentional opening of the engine valves. Such unintentional valve opening may prevent engine cylinders or combustion chambers from being sealed during the compression stroke of engine operation. In order to compensate for thermal expansion and wear of the valve train components, internal combustion engines may include hydraulic lash adjusters to reduce clearance, or lash, between the valve train components.

Hydraulic lash adjusters employ hydraulic fluid, such as, engine lubricating oil, to vary a length of the lash adjuster to compensate for the expansion of valve train components due to thermal effects. In particular, hydraulic lash adjusters operate by transmitting rotational energy of the camshaft through hydraulic fluid trapped in a high pressure volume beneath a piston. As the length of valve train components varies during operation of the camshaft, small quantities of hydraulic fluid are permitted to enter or escape the high pressure volume beneath the piston. As the hydraulic fluid enters or escapes the high pressure volume, the position of the piston is adjusted. This results in adjustment of the effective length of the valve train, thereby eliminating the lash.

Typically, hydraulic lash adjusters include oil recirculation grooves formed on the exterior of the piston. The oil recirculation groove allows hydraulic fluid to return to the inside of the piston. However, recirculation of the hydraulic fluid may cause overheating and discoloration of the hydraulic lash adjuster.

In addition, the valve train may include pushrods that are made of multiple parts joined together in a press fit assembly. When pressed together during assembly, material within the parts of the pushrod may be plowed and displaced due to the design of the parts. This may compromise the press fit and cause the pushrod assembly to become loose over time.

A pushrod for an internal combustion engine is disclosed in U.S. Pat. No. 5,720,246, entitled, “Continuous Fiber Reinforced Aluminum Matrix Composite Pushrod.” The '246 patent describes a pushrod formed of a continuous fiber reinforced aluminum matrix composite tube that has an aperture through which a coolant fluid could pass. The '246 pushrod further includes end caps formed of hardened steel that also include apertures to allow for passage of the coolant. While effective, further improvements in valve train components, such as hydraulic lash adjusters and pushrods, are still desired.

SUMMARY OF THE DISCLOSURE

In accordance with one embodiment, a pushrod assembly for an engine is disclosed. The pushrod assembly may include a first piece configured to house a hydraulic lash adjuster and a second piece coupled to the first piece. The first piece may include a mating portion with a tapered end section. The second piece may include a first bore adapted to receive the mating portion of the first piece.

In accordance with another embodiment, a valve train for an engine is disclosed. The valve train may include a camshaft, a lifter in contact with the camshaft, and a pushrod assembly mounted on the lifter. The pushrod assembly may be operatively configured to translate motion from the camshaft to a rocker for actuation of a valve. The pushrod assembly may include a hydraulic lash adjuster operatively connected to the rocker, and a first piece configured to house the hydraulic lash adjuster. The first piece may include a mating portion with a tapered end section. The pushrod assembly may also include a second piece coupled to the first piece, the second piece extending from a first end to a second end. The first end may include a first bore adapted to receive the mating portion of the first piece, the first bore including a curved end surface.

In yet another embodiment, a method for constructing a pushrod assembly is disclosed. The method may include leading a tapered end section of a first piece of the pushrod assembly into a first bore of a second piece of the pushrod assembly, the first piece including a hydraulic lash adjuster, a diameter of the tapered end section being less than a diameter of the first bore; and coupling the first piece to the second piece via a press fit engagement between a mating portion of the first piece and the first bore of the second piece.

These and other aspects and features will become more readily apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings. In addition, although various features are disclosed in relation to specific exemplary embodiments, it is understood that the various features may be combined with each other, or used alone, with any of the various exemplary embodiments without departing from the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of part of an engine, constructed in accordance with an embodiment of the present disclosure;

FIG. 2 is a schematic view of a pushrod assembly for the engine of FIG. 1;

FIG. 3 is a side view of a piston for a hydraulic lash adjuster in the pushrod assembly of FIG. 2;

FIG. 4 is a side view of a mating portion of a first piece in the pushrod assembly of FIG. 2;

FIG. 5 is an enlarged view of region 5 in the pushrod assembly of FIG. 2;

FIG. 6 is an enlarged view of region 6 in the pushrod assembly of FIG. 2; and

FIG. 7 is a flowchart illustrating a process for constructing a pushrod assembly, in accordance with yet another embodiment.

While the present disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof will be shown and described below in detail. The disclosure is not limited to the specific embodiments disclosed, but instead includes all modifications, alternative constructions, and equivalents thereof.

DETAILED DESCRIPTION

The present disclosure provides a hydraulic lash adjuster (HLA) pushrod assembly for an internal combustion engine. The HLA is built into the pushrod assembly, and the design of the HLA pushrod assembly includes a multi-piece press fit configuration. The pieces of the HLA pushrod assembly may have tapered end sections to minimize plowed material during assembly, as well as curved end surfaces in the bores to reduce stress concentration. In addition, the piston of the HLA may be groove-less in order to prevent oil from recirculating back into the HLA, thereby eliminating overheating and thermal discoloration associated with an oil recirculation groove.

Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Generally, corresponding reference numbers will be used throughout the drawings to refer to the same or corresponding parts.

FIG. 1 illustrates a cross-sectional view of part of an engine 20 consistent with certain embodiments of the present disclosure. The engine 20 may be used in any type of vehicle or machine that performs a driven operation involving physical movement associated with a particular industry, such as, without limitation, transportation, mining, construction, landscaping, forestry, agriculture, etc. Non-limiting examples of vehicles and machines, for both commercial and industrial purposes, include locomotives, vehicles, loaders, excavators, dozers, motor graders, tractors, trucks, backhoes, agricultural equipment, material handling equipment, marine vessels, and other types that operate in a work environment. It is to be understood that the engine 20 is shown primarily for illustrative purposes to assist in disclosing features of various embodiments, and that FIG. 1 does not depict all of the components of an engine.

The engine 20 may include a valve train 22, in accordance with an embodiment of the present disclosure. Although not shown, the engine 20 may include an engine block defining a plurality of cylinders. Each cylinder may contain a piston that reciprocates within the cylinder to generate mechanical energy from the chemical energy produced through combustion of a fuel within a combustion chamber of the cylinder. Each piston may be connected to a common crankshaft through a connecting rod, such that reciprocating movement of the pistons is translated into rotational motion to produce useful work in a machine with which the engine 20 is associated.

A cylinder head 24 may be bolted to the engine block to seal the cylinders. The cylinder head 24 may include valves 26, such as, at least one intake valve and at least one exhaust valve for each cylinder. Each valve 26 may include a valve head 28, a valve stem 30, and a valve spring 32 adapted to close and seal the valve 26. To open the valves 26, a camshaft 34 may be rotated such that a lobe 36 pushes against a lifter 38 and, through a series of actuation linkages, pushes the valves 26 open.

More specifically, the valve train 22 may further include a pushrod assembly 40 mounted on the lifter 38 and configured to translate motion from the camshaft 34 to a rocker 42. When the lobe 36 pushes against the lifter 38, the rocker 42 may be pivoted about a rocker shaft 44 by the pushrod assembly 40. The pivoting movement of the rocker 42 may actuate the valves 26, pushing the valves 26 open against the bias of the valve springs 32. When the lobe 36 rotates away from the lifter 38, the valves 26 are closed by the biasing force of the valve springs 32. Although a specific valve train 22 is shown and described, it is to be understood that different valve train configurations may be used.

Turning now to FIGS. 2 and 3, with continued reference to FIG. 1, the pushrod assembly 40 may comprise a first piece 46, a second piece 48, and a third piece 50 coupled together in a press fit engagement. The first piece 46 may comprise a body 52 and a mating portion 54. The body 52 of the first piece 46 may be configured to house a hydraulic lash adjuster (HLA) 56, which is operatively connected to the rocker 42. The HLA 56 may protect components of the valve train 22 from the engine's normal thermal expansion and wear processes by using hydraulic fluid to eliminate clearance or lash between valve train components. The HLA 56 may be incorporated with the pushrod assembly 40 between the lifter 38 and the rocker 42. However, the HLA 56 may be incorporated into the valve train 22 at other locations as well.

The body 52 of the first piece 46 may define an axial bore 58 having an open end 60 and a closed end 62. Defining a fluid reservoir 64, a hollow piston 66 may be telescopically received within the axial bore 58. The piston 66 may have a first end 68 disposed within the axial bore 58 and a second end 70 extending outwardly beyond the open end 60 of the body 52. A snap ring 72, or other type of retention element, may control travel of the piston 66 relative to the body 52. A high pressure volume 74 may be defined by the axial bore 58 and the first end 68 of the piston 66. A valve mechanism may regulate a fluid path from the fluid reservoir 64 to the high pressure volume 74.

A portion 76 of the piston 66 that is disposed within the axial bore 58 of the body 52 may be shaped and sized to provide a desired clearance, and thus, desired leakage from the high pressure volume 74 to an exterior of the HLA 56. More specifically, the desired clearance may define a leak path 78 extending from the high pressure volume 74 to the exterior of the HLA 56 along an exterior 80 of the piston 66. In order to prevent hydraulic fluid recirculation within the HLA 56, the piston 66 may be groove-less. Compared to HLA pistons of the prior art, the exterior 80 of the piston 66 may have no grooves for hydraulic fluid recirculation.

The exterior 80 of the piston 66 may be smooth and continuous from the first end 68 to the second end 70. There may be no grooves or passages on the exterior 80 of the piston 66, thereby blocking fluid communication from the leak path 78 to the fluid reservoir 64 interior of the piston 66. In so doing, hydraulic fluid cannot recirculate back inside the piston 66 from the exterior 80 of the piston. With the groove-less design of piston 66, hydraulic fluid escapes to the exterior of the HLA 56 in order to maintain cool temperatures of the HLA 56.

Referring now to FIGS. 4 and 5, with continued reference to FIGS. 1-3, the mating portion 54 may be configured to engage with the second piece 48 of the pushrod assembly 40. The mating portion 54 of the first piece 46 may include an edge 82, a middle section 84, and a tapered end section 86. The middle section 84 of the mating portion 54 may be generally cylindrical in shape and extend axially from the edge 82. In addition, the edge 82 and the middle section 84 may include a mating surface 90 that is in contact with the first bore 88 of the second piece 48. The second piece 48 may include a first bore 88 adapted to receive the mating portion 54 of the first piece 46. More specifically, the first bore 88 may include a mating section 92 that is generally cylindrical in shape. The mating section 92 of the first bore 88 and the edge 82 and the middle section 84 of the first piece 46 may be compressed together in a press fit.

Furthermore, the tapered end section 86 of the mating portion 54 may aid alignment during press fit construction of the pushrod assembly 40. The tapered end section 86 may gradually decrease in cross-sectional area from the middle section 84 to an end 94 of the first piece 46. For example, the tapered end section 86 may be generally conical in shape. Any diameter D₁ of the tapered end section 86 throughout a length L of the tapered end section 86 may be less than a diameter D₂ of the mating section 92 of the first bore 88. Dimensions of the tapered end section 86 may be determined through finite element analysis of various tolerance conditions. In addition, the end 94 of the first piece 46 may include a chamfered edge 96.

The first bore 88 of the second piece 48 may further include a curved end surface 98 in order to reduce stress concentration within the first bore 88. The curved end surface 98 may be generally hemispherical or partially spherical in shape. Extending from the mating section 92 to the curved end surface 98, an end section 100 of the first bore 88 may include a gap 102 between the curved end surface 98 of the second piece 48 and the end 94 of the first piece 46. The end section 100 may gradually decrease in diameter from the mating section 92 to the curved end surface 98. For example, the end section 100 may be generally conical in shape and may include a slight curvature 104 adjacent to the mating section 92. In so doing, the end section 100 may provide a smooth transition from the mating section 92 to the curved end surface 98. Thus, the end section 100 and curved end surface 98 may be smooth and rounded for a uniform stress distribution within the first bore 88.

Turning now to FIG. 6, with continued reference to FIGS. 1-5, the third piece 50 may include mating portion 54 identical to that of the first piece 46, including edge 82, middle section 84, tapered end section 86, mating surface 90, end 94, and chamfered edge 96. Furthermore, the second piece 48 may include a second bore 106 identical to the first bore 88, including mating section 92, curved end surface 98, end section 100, gap 102, and slight curvature 104. The second bore 106 may be adapted to receive the mating portion 54 of the third piece 50. More specifically, the second piece 48 may extend from a first end 108 (FIG. 2) to a second end 110 (FIG. 2), with the first bore 88 positioned at the first end 108 and the second bore 106 positioned at the second end 110. The mating portion 54 of the third piece 50 and the second bore 106 of the second piece 48 may have a mirrored geometry of the mating portion 54 of the first piece 46 and the first bore 88 of the second piece 48. In so doing, the second piece 48 and the third piece 50 may be coupled together in a press fit with a tapered end section 86 aiding in alignment during press fit construction of the pushrod assembly 40.

INDUSTRIAL APPLICABILITY

In general, the foregoing disclosure finds utility in various industrial applications, such as, in transportation, mining, earthmoving, construction, industrial, agricultural, and forestry vehicles and machines. In particular, the disclosed pushrod assembly may be applied to engines of vehicles, machines, locomotives, loaders, excavators, dozers, motor graders, tractors, trucks, backhoes, agricultural equipment, material handling equipment, marine vessels, and the like. Applying the disclosed pushrod assembly to an engine eliminates issues of overheating and thermal discoloration in the hydraulic lash adjuster (HLA). In particular, the piston of the HLA is groove-less, thereby preventing oil recirculation and maintaining cool temperatures in the HLA.

Furthermore, the pieces of the disclosed pushrod assembly allow for a more robust press fit configuration. For instance, the disclosed pushrod assembly includes tapered end sections and curved surfaces. When inserting the mating portions of the first and third pieces into the first and second bores, respectively, of the second piece, leading with a tapered end section minimizes plowed material of the bores, thereby ensuring a secure press fit. Moreover, smooth curved surfaces within the bores significantly reduce stress concentration and provide for a uniform stress distribution.

Turning now to FIG. 7, with continued reference to FIGS. 1-6, a flowchart illustrating an example process 120 for constructing the pushrod assembly 40 is shown, according to another embodiment of the present disclosure. The process 120 may comprise leading the tapered end section 86 of the first piece 46 of the pushrod assembly 40 into the first bore 88 of the second piece 48 of the pushrod assembly 40, at block 122. At block 124, the first piece 46 may be coupled to the second piece 48 via a press fit engagement between the mating portion 54 of the first piece 46 and the first bore 88 of the second piece 48. It is to be understood that the flowchart in FIG. 7 is shown and described as an example only to assist in disclosing the features of the disclosed system, and that more or less steps than that shown may be included in the method corresponding to the various features described above for the disclosed system without departing from the scope of the disclosure.

While the foregoing detailed description has been given and provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims appended hereto. Moreover, while some features are described in conjunction with certain specific embodiments, these features are not limited to use with only the embodiment with which they are described, but instead may be used together with or separate from, other features disclosed in conjunction with alternate embodiments. 

What is claimed is:
 1. A pushrod assembly for an engine, comprising: a first piece configured to house a hydraulic lash adjuster, the first piece including a mating portion with a tapered end section; and a second piece coupled to the first piece, the second piece including a first bore adapted to receive the mating portion of the first piece.
 2. The pushrod assembly of claim 1, wherein the mating portion includes a middle section having a mating surface in press fit engagement with a mating section of the first bore.
 3. The pushrod assembly of claim 2, wherein the tapered end section decreases in cross-sectional area from the middle section to an end of the first piece.
 4. The pushrod assembly of claim 3, wherein a diameter of the tapered end section is less than a diameter of the mating section of the first bore.
 5. The pushrod assembly of claim 4, wherein the end of the first piece includes a chamfered edge.
 6. The pushrod assembly of claim 5, wherein the first bore includes a curved end surface.
 7. The pushrod assembly of claim 6, wherein the curved end surface of the first bore is generally hemispherical in shape.
 8. The pushrod assembly of claim 7, wherein the first bore further includes a gap between the curved end surface and the end of the first piece.
 9. The pushrod assembly of claim 8, wherein the first bore gradually decreases in diameter from the mating section to the curved end surface.
 10. The pushrod assembly of claim 9, further comprising a third piece coupled to the second piece, the third piece including a mating portion with a tapered end section.
 11. The pushrod assembly of claim 10, wherein the second piece includes a second bore adapted to receive the mating portion of the third piece, the second bore including a curved end surface.
 12. The pushrod assembly of claim 11, wherein the hydraulic lash adjuster includes a groove-less piston to prevent recirculation of hydraulic fluid.
 13. A valve train for an engine, the valve train comprising: a camshaft; a lifter in contact with the camshaft; and a pushrod assembly mounted on the lifter and operatively configured to translate motion from the camshaft to a rocker for actuation of a valve, the pushrod assembly including: a hydraulic lash adjuster operatively connected to the rocker, a first piece configured to house the hydraulic lash adjuster, the first piece including a mating portion with a tapered end section, a second piece coupled to the first piece, the second piece extending from a first end to a second end, the first end including a first bore adapted to receive the mating portion of the first piece, the first bore including a curved end surface.
 14. The valve train of claim 13, wherein the hydraulic lash adjuster includes a piston, an exterior of the piston having no grooves for hydraulic fluid recirculation.
 15. The valve train of claim 14, wherein the exterior of the piston is smooth and continuous from a first end of the piston to a second end of the piston.
 16. The valve train of claim 15, wherein the pushrod assembly further includes a third piece coupled to the second piece, the third piece including a mating portion with a tapered end section, the second end of the second piece including a second bore adapted to receive the mating portion of the third piece, the second bore including a curved end surface.
 17. The valve train of claim 16, wherein each of the mating portions of the first piece and the third piece includes a middle section having a mating surface in press fit engagement with a mating section of each of the first bore and the second bore, respectively.
 18. The valve train of claim 17, wherein each of the tapered end sections of the first piece and the third piece decreases in cross-sectional area to an end of each of the first piece and the third piece, respectively.
 19. The valve train of claim 18, wherein a diameter of each of the tapered end sections of the first piece and the third piece is less than a diameter of the mating section of each of the first bore and the second bore, respectively.
 20. A method for constructing a pushrod assembly, the method comprising: leading a tapered end section of a first piece of the pushrod assembly into a first bore of a second piece of the pushrod assembly, the first piece including a hydraulic lash adjuster, a diameter of the tapered end section being less than a diameter of the first bore; and coupling the first piece to the second piece via a press fit engagement between a mating portion of the first piece and the first bore of the second piece. 